1. Field
Exemplary embodiments of the present invention relate to semiconductor design technology, and more particularly to a receiver circuit with a de-emphasis function.
2. Description of the Related Art
In integrated circuits, such as semiconductor memory devices, an operating voltage becomes lower, and a speed of transmitted signals gradually increases. When a transmitter transmits a digital signal through a channel having a loss, a receiver receives the transmitted signal in a state that is distorted depending on frequency components of the channel.
In general, since a channel has more losses in a high-frequency region, high-frequency components of a digital signal transmitted through the channel are attenuated more than low-frequency components. The high-frequency components in the digital signal correspond to voltage levels of the digital signal, which are changing rapidly, i.e., rising and falling edges. Accordingly, a waveform of the digital signal transmitted through the channel having a loss is distorted more than the original waveform, and the time at which the digital signal is arrived may differ depending on frequency components. As a result, lots of jitters may occur and overall timing margin may be reduced. Further, interference between the data, i.e., inter-symbol interference (ISI) arises. That is, since the time at which the digital signal is arrived may differ depending on frequency components due to the channel loss, successive data may overlap, which may result in incorrect delivery in a case of high-speed communication or a long-channel communication.
To resolve these concerns, the receiver circuit emphasizes or suppresses a signal depending on a frequency band to compensate for distortions that are generated through the channel having a loss, and controls a waveform of the signal so that the receiver circuit may receive the original waveform of the signal. Such a technique is called “equalization” such as a pre-emphasis method and a de-emphasis method.
FIGS. 1A and 1B are diagrams for explaining a pre-emphasis method and a de-emphasis method for a conventional receiver circuit.
Referring to FIG. 1A, in the pre-emphasis method, when a signal transits to a logic high/low level from a logic low/high level, a forepart of the transited signal is emphasized. That is, when the signal transits to a logic high level from a logic low level, a forepart of the logic high level of the transited signal is set to a voltage level higher than a target voltage at a logic high level (see numeral references 11 and 12). Further, when the signal transits to a logic low level from a logic high level, a forepart of the logic low level of the transited signal is set to a voltage level lower than a target voltage at a logic low level (see numeral references 13 and 14). In the pre-emphasis method, a level of the signal is emphasized at edges of the signal in consideration of an attenuation of the channel loss since the high-frequency components of the signal mainly remain on the edges.
Referring to FIG. 1B, in the de-emphasis method, when a signal transits to a logic high/low level from a logic low/high level, a rear part of the transited signal is de-emphasized. That is, when the signal transits to a logic high level from a logic low level, a rear part of the logic high level of the transited signal is set to a voltage level lower than a target voltage at a logic high level (see numeral references 15 and 16). Further, when the signal transits to a logic low level from a logic high level, a rear part of the logic low level of the transited signal is set to a voltage level higher than the target voltage at a logic low level (see numeral references 17 and 18). In the de-emphasis method, a level of the signal is relatively emphasized on edges of the transited signal in comparison with rear parts of the transited signal, and thus equalization may be secured when an amplitude of the signal is attenuated due to the high-frequency components remaining on the edges of the transited signal.
In designing the receiver circuit of an integrated circuit, developing a technology to implement a de-emphasis equalization method is in demand.